There are needs in the art for a web comprising mutually sequentially disposed pockets in which the web is disposed to be moved along mechanical retainer devices which, during a part of the displacement, hold the pockets in the opened position in order to make it possible to supply material into the pockets, whereafter the retainer devices, on continued movement of the web, hold the pockets in a position in which closure of the pockets takes place.
Patent specification EP-B1 0 054 564 describes a web of the above-indicated type. The web displays two opposing walls and longitudinal first (lower) and second (upper) edges. The web comprises mutually sequentially disposed pockets, with a bottom portion at the first edge and two connecting zones which are transverse in relation to the longitudinal direction of the web and which form side closures of the pockets. Transverse slits are provided between the connecting zones in two adjacent pockets in order to separate the pockets from one another.
The web according to EP-B1 0 054 564 includes two substantially opposing strip portions which extend in the longitudinal direction of the web at its above-mentioned second edge. Each strip portion is provided with a continuous retainer device for cooperation with mechanical guide means for holding the strip portions in spaced apart relationship from one another and thereby holding the pockets in opened position in connection with material being supplied into the pockets. In both walls, the web is provided with slits disposed in the longitudinal direction of the web, the slits for each wall being symmetrically located on either side of the transverse slits.
In purely practical terms, it has proved that the walls of the web in the web described in EP-B1 0 054 564, on movement along the mechanical retainer devices, show a tendency to undesirable displacement in relation to one another in the longitudinal direction of the web. When such mutually displaced walls are moved to positions adjacent to one another for closure of the pockets, creases are readily formed in those regions where the closure is to take place. Such crease formations generally entail that an unacceptable closure is formed on fusion of the strip walls. A further drawback inherent in the prior art web is that the edges located transversely of the longitudinal direction of the web often form undesirable inward or outward bulges in the opened pockets. Such inward and outward bulges lead to problems in the supply of material into the pockets, for which reason correction must be made of the shape of the openings using mechanical devices which are introduced down into the openings and move the edges to positions in which filling and closure of the pockets are not jeopardized.